Dry etches are frequently used during semiconductor manufacturing processes. When a dry etch is to be carried out, the etching method and the method for removing the etch residue material have to be properly selected in accordance with the object to be etched. A conventional dry etching method is constituted as follows.
First, in the case where the object to be etched is a metal, the etch residue material is converted into a volatile material after etching, so that the etch residue material can be removed in the form of a gas.
That is, the etch residue material, which is formed by reaction between the etched material and the etch chemistry, is removed via a gaseous state. The etch chemistry is selected in such a manner that the etch residue material should have an increased volatility at the etching temperature, whereby the etch residue material becomes a compound which can be removed in a gaseous state.
For example, in the case where Al is to be etched by using F.sub.2 gas, a reaction occurs may be illustrated as follows.
Al+3F.fwdarw.AlF.sub.3. PA1 Al+3/2Cl.sub.2 .fwdarw.AlCl.sub.3 (.uparw.) PA1 SiO.sub.2 +CF.sub.4 .fwdarw.SiF.sub.4 +CO.sub.2 (.uparw.) PA1 Residue materials containing C and F+O.sub.2 plasma.fwdarw.COF, CO, CO.sub.2. PA1 Residue material/lower layer Si+HBr/Cl.sub.2 plasma.fwdarw.residue material/(SiBr.sub.4, SiCl.sub.4). PA1 Polymer+O.sub.3 /H.sub.2 SO.sub.4 .fwdarw.CO.sub.2 PA1 Polymer+H.sub.2 O.sub.2 /H.sub.2 SO.sub.4 .fwdarw.CO.sub.2 PA1 Residue materials/lower layer SiO.sub.2 .fwdarw.residue materials/Si.sub.2 F.sub.6 H.sub.2 PA1 Residue materials/lower layer SiO.sub.2 +BOE.fwdarw.residue materials/Si.sub.2 F.sub.6 H.sub.2
However, AlF.sub.3 is not volatile at a normal temperature, but becomes volatile at a temperature of over 200.degree. C. Therefore it is not used.
If chlorine Cl.sub.2 gas is used as the etching chemistry, there is formed AlCl.sub.3, which is highly volatile at a normal temperature, and therefore, this material is widely used. The reaction may be illustrated as follows.
Therefore, when Al is etched, a chemistry of Cl.sub.2 gas typically is used. If this method is used, however, an etch residue material is formed simultaneously with the formation of AlCl.sub.3. Accordingly, there is required an additional process for removing the etch residue material. Due to the properties of the metal, an acid cannot be used for removing the etch residue material, and it has been difficult to remove the residue material.
Further, in the case where the etched material is silicon oxide, the used chemistry typically is CF.sub.4 or CHF.sub.3, and with this chemistry, a dry etching is carried out. In this case, an example reaction may occur as illustrated as follows:
Based on the above illustrative reaction, SiF.sub.4 is formed, but other materials including etch residue materials such as CF, CF.sub.2 and CF.sub.3 also tend to form, and, therefore, a process for removing etch residue material also has to be carried out.
As for methods of removing etch residue materials formed after an etching process, there are dry chemical methods and wet chemical methods.
A dry chemical method is that in which a dry chemical of a plasma state is used to remove the etch residue materials including C and F. With such a method, the etch residue materials and the dry chemical of a plasma state directly react to form a highly volatile material, thereby removing the etch residue materials. Alternatively, a lift-off method in which the silicon of a lower layer under the residue material is etched, thereby removing the etch residue material utilizing a lift-off phenomenon.
The reaction in such cases may be illustrated as follows.
In the wet chemical method for removing the etch residue materials, a U cleaning+a D cleaning may be applied, in which a sulfuric acid chemical, a developer (containing amine as the main ingredient) and hydrogen peroxide are used, thereby removing polymers of a large molecular size. In the case where the lower layer consists of an oxide film, HF or a BOE (buffered oxide etchant) may be used. The U cleaning may use a solution in which NH.sub.4 OH, H.sub.2 O.sub.2 and H.sub.2 O are mixed at a ratio of 1:2:10, or 1:1:5, while the D cleaning may use a solution in which HCl, H.sub.2 O.sub.2 and H.sub.2 O are mixed at a ratio of 1:1:5. In both the U cleaning and the D cleaning, a cleaning is carried out, for example, at 10 minutes at a temperature of 80.degree. C. The reactions for removing residue materials by using a wet chemical method may be illustrated as follows.
In conventional methods as described above, if a polymer of a large molecular size is to be removed, there typically is required a composite process consisting of an oxygen plasma+U cleaning+D cleaning, or O.sub.3 /H.sub.2 SO.sub.4 +U cleaning+D cleaning.
Further in the case where a polymer is disposed upon a metal, if the general acid or the U cleaning is applied, the metal is corroded, and, therefore, basically developers have been used. However, defects due to the metal corrosion tend to remain as before.